Confirmed by science: France saves heating and cooling costs with the warm edge 4 February 2019 Back to news index

Small component, big impact

Confirmed by science: France saves heating and cooling costs with the warm edge

A scientific study now shows with concrete figures how much heating and cooling costs French home-owners and tenants can save with plastic spacer bars in the insulating glass in heat insulating windows.

In modern heat insulating windows, after the glass and frame, the spacer bar is the third important component in terms of the energy performance. The spacer bar is now really becoming the centre of attention. If the spacer bar has a poor – i.e. high – heat transmission coefficient, a lot of heat is lost to the outside – even with an excellent frame and high-tech glass. Even with the plastic spacer bars, there are big differences in the performance values: A highly efficient warm edge, as used in the study, has a linear thermal conductivity of 0.14 W/(mK). The value for stainless steel is 0.6 and for the aluminium spacer bar – the clear back marker – it is a massive 160 W/(mK).

Three French reference cities that represent three different climate zones were chosen: Nancy for the cool-temperate climate, La Rochelle for the warm-temperate climate and Nice for the warm climate zone.

The new study of the independent Passive House Institute also calculates the savings of heating and cooling energy and CO2 emissions of entire buildings thanks to the small, efficient component. The results confirm the great benefits of high-quality plastic spacer bars compared with spacers made of aluminium.

The new study by the Passive House Institute was the first to investigate the influence of the spacer bars on the annual heating requirements of buildings: The study compares aluminium, stainless steel and plastic spacer bars in the windows of common houses that meet the requirements of the French energy standards in three different climate zones.  The results: If high-quality plastic spacer bars are used instead of aluminium spacer bars, in the cool-temperate climate in Nancy, 5.9 percent of the total heating energy can be saved in a standard French house with double glazing. With a conventional house with ever more commonly used triple glazing, as much as 7.9 percent can be saved, and in a building following the Passive House standard, the savings are nearly 18 percent.

In the warm-temperate climate zone in La Rochelle, in the case of a typical country house with double glazing, the savings are 4.2 percent, with 5.7 percent savings in a house with triple glazing and in the passive house, over 13 percent can be saved.

In the warm climate of Nice, in addition to the 49.6 kWh/(m²a) annual heating requirement with aluminium spacer bars, there is also a useful cooling requirement – energy needed for cooling provided by the air conditioning unit in summer – of 33.3 kWh/(m²a) at 20 °C maximum internal temperature.

The energy savings are lower in comparison to the climates where only heating is required, with savings of up to 3.8 percent by using the plastic spacer bar instead of the aluminium spacer, but a maximum of just under 9 percent in the passive house.

The study was commissioned by SWISSPACER, one of the producers of warm edge spacer bars. “With the scientific investigation by an independent research institute, we wanted resilient data for the market," stressed Andreas Geith, Managing Director of SWISSPACER.


For more information, visit The complete study is also available for download there.